Yes, that path is: puppet:///modules/${module_name}/puppet.conf.
The triple slash expands to the server name.
And don't be tempted to put ${module_name}/files/puppet.conf in there.
The file/ is in the path to the file in the filesystem of the server, but it is not in the path when being accessed through the Puppet protocol.

So far for configuration logic.

... and /srv/puppet/envs/production/modules/puppet_agent/files/puppet.conf: